The present invention relates to a moving target indication unit provided with a bank of Doppler filters with n output channels A.sub.i (i=0, 1, 2, . . . , n-1), several threshold circuits connected to the output channels, a detection and registration unit provided with means for determining and storing, per azimuth cell, a parameter for the amount of clutter in the azimuth cell, and for setting the threshold circuits per azimuth cell on the basis of the parameter.
In such a known system, the output signal of filter channel 0, the channel with Doppler speeds of around 0 Hz, is used to estimate a parameter of the amount of clutter in an azimuth cell. This value is subsequently stored in a memory. To obtain a parameter for the amount of clutter in the remaining filter channels, a fixed functional connection is assumed between, on the one hand, the amount of clutter in output channel 0 and, on the other hand, the amount of clutter in the remaining channels. In other words a distribution of the clutter across the different channels is assumed. This implies that an estimation is made of the amount of clutter in the filter channels A.sub.i (i=1, 2, . . . , n-1). It has been proven in practice that clutter suppression is not always effective. The inventor found that this is caused by the fact that the clutter distribution across the different output channels A.sub.i is dependent on the type of clutter confronted. Different types of clutter occur especially in the case of search radars, where the radar covers different types of territories, e.g. land and sea clutter. Different types of clutter also occur as a result of variable weather conditions.